Previous literature suggests that a disturbed ability to accurately identify own body size may
contribute to overweight. Here, we investigated the influence of personal body size, indexed
by body mass index (BMI), on body size estimation in a non-clinical population of females
varying in BMI. We attempted to disentangle general biases in body size estimates and attitudinal
influences by manipulating whether participants believed the body stimuli (personalized
avatars with realistic weight variations) represented their own body or that of another
person. Our results show that the accuracy of own body size estimation is predicted by personal
BMI, such that participants with lower BMI underestimated their body size and participants
with higher BMI overestimated their body size. Further, participants with higher BMI
were less likely to notice the same percentage of weight gain than participants with lower
BMI. Importantly, these results were only apparent when participants were judging a virtual
body that was their own identity (Experiment 1), but not when they estimated the size of a
body with another identity and the same underlying body shape (Experiment 2a). The different
influences of BMI on accuracy of body size estimation and sensitivity to weight change
for self and other identity suggests that effects of BMI on visual body size estimation are
self-specific and not generalizable to other bodies.

Background: Body image disturbance (BID) is a core symptom of anorexia nervosa (AN), but as yet distinctive features of BID are unknown. The present study aimed at disentangling perceptual and attitudinal components of BID in AN. Methods: We investigated n=24 women with AN and n=24 controls. Based on a 3D body scan, we created realistic virtual 3D bodies (avatars) for each participant that were varied through a range of ±20% of the participants' weights. Avatars were presented in a virtual reality mirror scenario. Using different psychophysical tasks, participants identified and adjusted their actual and their desired body weight. To test for general perceptual biases in estimating body weight, a second experiment investigated perception of weight and shape matched avatars with another identity.
Results: Women with AN and controls underestimated their weight, with a trend that women with AN underestimated more. The average desired body of controls had normal weight while the average desired weight of women with AN corresponded to extreme AN (DSM-5). Correlation analyses revealed that desired body weight, but not accuracy of weight estimation, was associated with eating disorder symptoms. In the second experiment, both groups estimated accurately while the most attractive body
was similar to Experiment 1.
Conclusions: Our results contradict the widespread assumption that patients with AN overestimate their body weight due to visual distortions. Rather, they illustrate that BID might be driven by distorted attitudes with regard to the desired body. Clinical interventions should aim at helping patients with AN to change their desired weight.

Our goal is to understand the principles of Perception, Action and Learning in autonomous systems that successfully interact with complex environments and to use this understanding to design future systems